Human cervical epithelium can elaborate a series of progressive neoplastic changes known as cervical dysplasia or cervical intraepithelial neoplasia (CIN), which are precursors to invasive cervical cancer. The designations CIN I, II and III refer to mild, moderate, and severe dysplasia/carcinoma in situ, respectively. This histological grading scheme is based largely on the extent to which the thickness of the epithelium is replaced by mitotically active cells with enlarged, hyperchromatic nuclei [1]. Untreated, a subset of dysplastic lesions will advance to cancer, with a frequency that increases dramatically in CIN III lesions [2]. Infection with the human papillomavirus (HPV) is strongly correlated with the development of cervical cancer [3, 4]. HPV is present in over 90% of CIN lesions [5], 95% of cervical cancer [4], and 93% percent of anal squamous cancers in women [6].
In many developing countries, cervical cancer is the most common cancer (excluding skin) in women and the major cause of cancer-related deaths in women [7]. In the United States, abnormalities on Papanicolaou, or "Pap" smears are detected in millions of women annually, resulting in an estimated annual cost of $6 billion for patient evaluation and treatment [8]. The success of Pap smear screening is reflected by the fact that there are only approximately 15,000 new cases of cervical cancer annually in the United States. Indeed, a significant body of evidence supports the observation that population-based Pap smear screening can significantly reduce the incidence of cervical cancer between 3 and 10-fold [9]. Nevertheless, at least 10% of dysplasia cases are diagnosed as negative by Pap smear (false negative).
The Pap smear test consists of collecting cells from the cervix and vagina, spreading them onto a glass slide, fixing and staining the cells, and analyzing them under a microscope. Cytological features that distinguish dysplastic cells, such as enlarged hyperchromatic nuclei and increased nuclear/cytoplasmic ratio, are identified by visually scanning the entire slide. While the success of the Pap smear at detecting cervical precancers and cancers is irrefutable, the assay has several limitations: It is a sampling technique in which typically fewer than half of the cells collected from the cervix are transferred to the slide for analysis, contributing to false negative test results. It is dependent upon human observers to read each cell on the slide, generating another source of false negative results due to observer error. It has a relatively long turn-around time, ranging from several days to weeks, impeding effective followup in much of the world. The test is relatively labor-intensive and requires trained personnel, making it unavailable as a screening test in many areas. Some of these limitations have recently been addressed by new technologies available in North America and Europe. Cytyc Corp has introduced an improved collection and slide preparation technique called the ThinPrep Test in which cells are collected into a liquid fixative rather than directly applied to a slide in the field, and delivery of the cells to the slide is performed mechanically, generating a random distribution of cells on the slide more representative of the original population of cells collected. The slides generated by this technology are easier to interpret microscopically, making the test more sensitive to abnormalities. Two companies have recently marketed computers based on neural network programming which digitally analyze cells on Pap smears and identify cells suspicious for dysplasia and cancer: these cells are then reinterpreted by a human observer. This technology is intended to reduce the false negative rate, and is currently only recommended for slides that have previously been analyzed in the conventional fashion and read out as negative.
Similarly, other attempts to identify noncytological markers of cervical dysplasia have only confirmed the need to supplement such assays with conventional cytological examination such as Pap smear to effect clinical diagnosis with tolerable accuracy, e.g. Kyo S et al. (1997) Application of telomerase assay for the screening of cervical lesions. Cancer Res 57(10), 1863-1867; Pillai MR (1996) The presence of human papillomavirus-16/-18 E6, p53, and Bc1-2 protein in cervicovaginal smears from patients with invasive cervical cancer. Cancer Epidemiol Biomarkers Prev 5(5), 329-335. Accordingly, an object of the invention is to provide a screening method amenable to wider, preferably ready, international availability, that can detect premalignant cervical disease before it becomes invasive without the need for any supplemental conventional cytological examination.